Telemetry, Witnesses Hold Clues to 525 Breakup

NTSB investigators are culling a wealth of data, including telemetry and eyewitness accounts from chase pilots, for clues as to why a Bell Helicopter 525 prototype disintegrated in flight July 6.

The distribution of wreckage on the ground indicates that the aircraft broke up in midair. In addition to the aft tailboom and empennage, which was found 1,500 ft from the main field of heavily burnt wreckage, pieces of shattered main rotor blades were found separated from the main wreckage field, which included remnants of much of the super-medium twin, its engine compartment and a gearbox.

The No. 1 prototype was transmitting telemetry to its launch point at Bell’s Xworx research center at Arlington, Texas, Municipal Airport during the flight that ended with its crash about 30 nm south-southwest of that facility. It also was being followed by a chase helicopter with two Bell pilots aboard during the accident flight. Bell has used a 429 as a chase aircraft for 525 flight tests.

A team of six investigators was dispatched from the National Transportation Safety Board’s Washington office to the crash, which involved the prototype for what Bell has described as the first commercial helicopter using all fly-by-wire flight controls.

The NTSB team is led by Investigator-in-Charge John Lovell and includes Chich Shin, who worked for the U.S. Navy as a helicopter transmissions systems engineer before joining the safety board in 2012, and Van McKinney, a helicopter specialist for the board. Their work is being supported by investigators from the FAA, Bell and General Electric (which makes the 525’s two CT7-2F1 engines).

Investigators are assessing the data in the telemetry from the 525 for information about the accident flight and previous flight tests of the aircraft. The NTSB retrieved a flight test recorder from the wreckage and sent to its Washington recorder lab for readout. The safety board described the recorder as being in good condition. But the NTSB has declined to say whether it has retrieved any data from that recorder.

Investigators also have interviewed the chase pilots, according to officials familiar with the probe, who said the chase crew recorded no video of the accident flight.

According to persons familiar with Bell’s flight test operations, the chase crew is responsible for tracking the test pilots’ execution of the test plan for a flight, which is detailed in a test card. One pilot focuses on flying the chase helicopter, verifying the test area is clear of aircraft other than the prototype and staying clear of the test aircraft while keeping it in sight.

The other pilot on the chase aircraft tracks the execution of the test card and maintains communications with air traffic control for the aircraft pair to free the 525 pilots to concentrate on the flight test.

The chase crew also is guiding the test crew to stay within the test box of airspace and to stay within line of sight with the Xworx, since the telemetry link is a line-of-sight one.